memblock: Make find_memory_core_early() find from top-down

That is used for find ram in node or bootmem type.

We should make it top-down so it will be consistent to memblock_find,
and to avoid allocating potentially valuable low memory before we
actually need it.

Suggested-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <4D0C075B.3040501@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

mm/page_alloc.c

@@ -3555,6 +3555,34 @@ static int __meminit next_active_region_index_in_nid(int index, int nid)
 	return -1;
 }
 
+/*
+ * Basic iterator support. Return the last range of PFNs for a node
+ * Note: nid == MAX_NUMNODES returns last region regardless of node
+ */
+static int __meminit last_active_region_index_in_nid(int nid)
+{
+	int i;
+
+	for (i = nr_nodemap_entries - 1; i >= 0; i--)
+		if (nid == MAX_NUMNODES || early_node_map[i].nid == nid)
+			return i;
+
+	return -1;
+}
+
+/*
+ * Basic iterator support. Return the previous active range of PFNs for a node
+ * Note: nid == MAX_NUMNODES returns next region regardless of node
+ */
+static int __meminit previous_active_region_index_in_nid(int index, int nid)
+{
+	for (index = index - 1; index >= 0; index--)
+		if (nid == MAX_NUMNODES || early_node_map[index].nid == nid)
+			return index;
+
+	return -1;
+}
+
 #ifndef CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID
 /*
  * Required by SPARSEMEM. Given a PFN, return what node the PFN is on.
@@ -3606,6 +3634,10 @@ bool __meminit early_pfn_in_nid(unsigned long pfn, int node)
 	for (i = first_active_region_index_in_nid(nid); i != -1; \
 				i = next_active_region_index_in_nid(i, nid))
 
+#define for_each_active_range_index_in_nid_reverse(i, nid) \
+	for (i = last_active_region_index_in_nid(nid); i != -1; \
+				i = previous_active_region_index_in_nid(i, nid))
+
 /**
  * free_bootmem_with_active_regions - Call free_bootmem_node for each active range
  * @nid: The node to free memory on. If MAX_NUMNODES, all nodes are freed.
@@ -3644,7 +3676,7 @@ u64 __init find_memory_core_early(int nid, u64 size, u64 align,
 	int i;
 
 	/* Need to go over early_node_map to find out good range for node */
-	for_each_active_range_index_in_nid(i, nid) {
+	for_each_active_range_index_in_nid_reverse(i, nid) {
 		u64 addr;
 		u64 ei_start, ei_last;
 		u64 final_start, final_end;